add everyting for docs

docs/snippets/modules/chains/base_class.mdx

@@ -0,0 +1,15 @@
+```python
+class Chain(BaseModel, ABC):
+    """Base interface that all chains should implement."""
+
+    memory: BaseMemory
+    callbacks: Callbacks
+
+    def __call__(
+        self,
+        inputs: Any,
+        return_only_outputs: bool = False,
+        callbacks: Callbacks = None,
+    ) -> Dict[str, Any]:
+        ...
+```